As a conventional inkjet recording method, a piezo method for jetting an ink droplet by changing a shape of an ink passage according to a vibration of a piezoelectric element, a thermal method for making a heat generator provided in an ink passage heat to generate air bubbles and jetting an ink droplet according to a pressure change by the air bubbles in the ink passage, and an electrostatic sucking method for charging ink in an ink passage to jet an ink droplet by an electrostatic sucking power of the ink are known (for example, see JP-Tokukaihei-8-238774A, JP-Tokukai-2000-127410 and JP-Tokukaihei-11-277747 (FIG. 2 and FIG. 3)).
Further, conventionally, for the purpose of preventing clogging, there is an inkjet recording apparatus for forming an image by supplying ink in which a color material is dispersed into a solvent, by liberating an electrostatic force to the color material component in the ink and by making an ink droplet fly to a recording medium, the inkjet recording apparatus comprising a voltage applying section for applying a voltage to a plurality of electrodes provided on a head base, the voltage stirring the color material component in the ink (for example, see JP-Tokukaihei-9-193392 (page 3 to 6, FIG. 2).
However, the above-mentioned inkjet recording method has the following problems.
(1) Limit and Stability of a Minute Liquid Droplet Formation
Since a nozzle diameter is large, a shape of a droplet jetted from a nozzle is not stabilized, and there is a limit of making a droplet minute.
(2) High Applying Voltage
For jetting a minute droplet, miniaturization of a jet opening of the nozzle is an important factor. In a principle of the conventional electrostatic sucking method, since the nozzle diameter is large, an electric field intensity of a nozzle edge portion is weak, and therefore, in order to obtain necessary electric field intensity for jetting a droplet, it is necessary to apply a high jetting voltage (for example, extremely high voltage near 2000[V]). Accordingly, in order to apply a high voltage, a driving control of a voltage becomes expensive, and further, there is a problem in the aspect of safety.
Further, a cleaning mechanism which is effective to an electrostatic sucking type inkjet array, represented by a slit jet, comprises at least one ink container volume change generating section for changing a meniscus position of ink of a common opening part (slit), and a section for wiping the common opening part with an elastic cleaning member in a slit direction on a regular or sequential basis, wherein, before the wiping by the wiping section, a volume of the ink container is increased, the meniscus position is drawn back more than a slit width length, preferably three times more than the slit width, from a slit position, and the section performs the wiping in the slit direction under the condition that ink liquid is not contacted with the cleaning member to eliminate stain and foreign material existing on a slit surface, for preventing clogging. In an electrostatic sucking type inkjet of a type comprising a minute nozzle or comprising a minute nozzle with an edge portion thereof protruding in the present invention, such a cleaning method generates unevenness of a cleaning property and therefore it is not preferable, and further, it is not possible to manage cleaning in the minute nozzle and cleaning a passage. Further, in regard to a nozzle hole type electrostatic sucking type inkjet array, there is a method for cleaning a nozzle outside surface. However, in regard to the type comprising a minute nozzle or comprising a minute nozzle with an edge portion thereof protruding, by only cleaning the outside surface, a cleaning unevenness is similarly generated and therefore it is not preferable, and it is not possible to deal with cleaning in the minute nozzle and cleaning the passage. Therefore, an object is to accurately clean the electrostatic sucking type inkjet comprising the minute nozzle or comprising the minute nozzle with the edge portion thereof protruding so as to make no influence on clogging and landing accuracy of droplet.
Further, if a liquid jetting apparatus is not used for a long time or a specific nozzle is not used for a long time due to an operational circumstance, there is the case that aggregates of fine particles are formed by aggregating fine particles contained in liquid solution in the nozzle or in a supplying passage for supplying the liquid solution to the nozzle. For example, when aggregates are formed in the nozzle, the aggregates are clogged at a liquid solution jet opening of the nozzle, and clogging of the nozzle occurs. Further, when aggregates are formed in the supplying passage, in conjunction with liquid solution supply to the nozzle at the time of image formation or the like, the aggregates are carried to a liquid solution jet opening of the nozzle, and the aggregates are clogged at the nozzle jet opening. Further, since aggregates easily adhere to an inside surface of the supplying passage, there is a possibility that supplying of liquid solution to the nozzle is not suitably performed due to a minified cross-sectional area of the supplying passage with the aggregates adhering to the inside surface of the supplying passage. Therefore, there was a problem that it was not possible to suitably perform a liquid solution jetting from a nozzle.
In particular, since super-miniaturization of a nozzle has been in progress in conjunction with formation of a high-resolution image these days, there is a state where clogging of the nozzle easily occurs due to aggregates of fine particles in the liquid solution.
Thereupon, to provide a liquid jetting apparatus capable of jetting a minute droplet is a first object. At the same time, to provide a liquid jetting apparatus capable of jetting a stable droplet is a second object. Further, to provide a liquid jetting apparatus capable of jetting a minute droplet and having good jetting accuracy is a third object. Further, to provide a liquid jetting apparatus in which it is possible to reduce an applying voltage, the liquid jetting apparatus being cheap and having high safety, is a fourth object. Further, since there is a concern that clogging of a nozzle occurs with high frequency in conjunction with a minute-diameter nozzle and with a large number of nozzles, to prevent clogging of a nozzle by suppressing liquid solution from adhering to a circumference of the nozzle to prevent the liquid solution from being fixed to the nozzle is a fifth object.